Improved electric switch ceramic contact supporting member

ABSTRACT

An electric switch having a dry electrically insulating film bonded permanently to one of two proximate facing surfaces of a pair of relatively movable ceramic members, such as facing generally cylindrical surfaces of rotor and stator members. The film reduces friction while acting as an electrical insulator and serves a very important function in preventing interengagement of the surfaces to thereby prevent the formation of ceramic dust particles which might otherwise engage between electrical contacts carried by the ceramic members. The film preferably is heat bonded to the surface and may comprise a tetrafluoroethylene (teflon) combined with either a bonding resin material or a water base with modifiers, or a molybdenum, tungsten or other metal sulfide combined with a sodium silicate or with isopropanol. Further important features relate to methods by which dry film lubricants of superior qualities are obtained, firmly bonded to the surface.

United States Patent [72] Inventor Aldrich John Zidlicky OTHER REFERENCES Whitefish y Oak Distributor Switches (Catalog), Effective Date June [21] Appl- N 728,507 1, 1962, p. 2, Dimensions Copy Available Class 200 Sub- [22] Filed May 13, 1968 class 11(D) [45] Patented Jan. 5, 1971 [73] Assignee clobfiunion In Pnrnary Examiner-Robert K. Schaefer Milwaukee Wis Assistant ExammerJ. R. Scott Attorney-Pendleton Neuman Williams & Anderson a corporation of Delaware 541 IMPROVED ELECTRIC SWITCH CERAMIC AESTRACT: An electric switch having a dry electrically insu- CONTACT SUPPORTING MEMBER latmg film bonded permanently to one of two proximate facmg surfaces of a pair of relatively movable ceramic members, 11 Claims, 4 Drawing FIgs.

such as facing generally cylindrical surfaces of rotor and stator [52] [1.5. CI 200/11, members The film reduces friction while acting as an elecui 252/12 cal insulator and serves a very important function in preventllllinterengagement f th surfaces t th by prevent th [50] F ield of Search 200/1 1D; formation of ceramic dust particles which might Otherwise em 252/12 gage between electrical contacts carried by the ceramic mem- 56 R ferences Cited bers. The film preferably is heat bonded to the surface and 1 e may comprise a tetrafluoroethylene (Teflon) combined with UNITED STATES PATENTS either a bonding resin material or a water base with modifiers, 2,440,037 4/1948 Wolff et al. 200/11(D)X or a molybdenum, tungsten or other metal sulfide combined 3,122,505 2/ 1964 Rulon-Miller et al 252/12 with a sodium silicate or with isopropanol. Further important 3,135,564 6/1964 Agens 252/12 features relate to methods by which dry film lubricants of su- 3,433,742 3/f 969 Banta 252/12 perior qualities are obtained, firmly bonded to the surface.

actuation, without requiring close manufacturing tolerances and with manufacturing expense being minimized.

Ceramic switches, i.e. switches wherein interengageable contacts are carried by ceramic parts, have advantages over other types of switches, but difficulties have been encountered with ceramic switches. In particular, the electrical switching action has not always been reliable and troubles have been experienced with regard to the force required to actuate the switches and with respect to noise.

This invention was evolved with the general object of overcoming the disadvantages of prior switch constructions and of providing switches which are quiet and easily operated while having high reliability.

Another object of the invention is to provide switches and methods of making the same to provide such advantages, but with minimum manufacturing expense and trouble.

The invention is based in part upon the discovery that the problems encountered with ceramic switches are due in large part to the rubbing contact between surfaces of relatively rotatable or otherwise relatively movable ceramic members. In particular, it has been foundl that the failure of switch contacts is oftentimes due to the lodging of ceramic particles between the engageable contacts and that such ceramic particles are formed by the abrasive action of interengaging ceramic parts. In addition, it has been found that the energy required to actuate the switches is increased substantially by the rubbing contact and varies to a considerable extent, resulting in faulty switch action in manylcases. Further, the rubbing of the surfaces has caused a gritting sensation, unpleasant to the ear and to the touch.

It is also found that it is extre ely difficult and virtually impossible in practice to maint in manufacturing tolerances which are sufficiently close to prevent the rubbing contact.

According to this invention, a dry electrically insulating film lubricant is permanently bonded to one of two proximate facing surfaces of a pair of relatively movable ceramic members, such as one of the facing generally cylindrical surfaces of rotor and stator members. The film lubricant reduces friction while acting as an insulator and serves a very important function in preventing interengagement of the surfaces to thereby prevent the formation of ceramic dust particles which might otherwise engage between electrical contacts carried by the ceramic members.

In addition, close manufacturing tolerances are not required.

The dry film lubricant is particularly advantageous in switch assemblies of the type in which various types of contacts are assembled, according to the functions which the switching assemblies do perform. In such switches, and particularly in rotary switches, an electrical contact or contacts may be secured to a rotor member which is keyed to an actuating shaft and it is desirable to allow a relatively loose fit in order to permit ready assembly of the switch. At the same time, it is desirable to eliminate any binding action which might cause canting of the member or otherwise cause malfunction of the switch. With the dry film lubricant, such difficulties are minimized.

In accordance with an important feature of the invention, the dry film lubricant is heat bonded to the surface of a ceramic part, to minimize peeling and to obtain long life.

One preferred composition of the dry film lubricant is a tetrafluoroethylene material (teflon) which has excellent electrical and lubricating properties and which is tough with a long life. The tetrafluoroethylene material may be combined with a 'water base with modifiers and, after applying an air drain, may

be fused and bonded to the surface bybaking at a relatively high temperature. Preferably, I however, the tetrafluoroethylene material is combined with a bonding resin, such as a phenolic resin or an epoxy resin, which, in accordance with the recommendations of suppliers, may be baked at a temperature on the order of from 300 to 350 F. It has been discovered, however, that superior results can be obtained by increasing the temperature to a temperature on the order of 500 F. or higher, or by performing a subsequent baking step at that temperature. Apparently, the resin material decomposes to a certain extent at the higher temperature and, in any event, a superior bonding of the material to the ceramic surface is obtained. l

Another preferred type of composition of the dry film lubricant is a molybdenum, tungsten or other metal sulfide combined with sodium silicate and water or with isopropanol. With sodium silicate, the parts may be preheated to a temperature on the order of 350 F. and then allowed to air dry, while with isopropanol, a simple air dry cure may be used.

In accordance with further features of the invention, the dry film lubricant is applied to generally cylindrical peripheral surfaces of ceramic rotor parts in the form of flat discs having central openings for passage of a support shaft therethrough. To apply the dry film lubricant, the rotor'parts are stacked on carrier rods in a manner such that only the peripheral surfaces to be coated are exposed, after which the dry film lubricant composition may be sprayed or otherwise applied on the exposed surfaces, the baking, drying or other processing steps being then performed.

This invention contemplates other objects, features and advantages which will become more fully apparent from the following detailed description taken in conjunction with the accompanying drawing which illustrates a preferred embodiment and in which:

FIG. 1 is a cross-sectional view of a switch assembly constructed in accordance with the principles of this invention;

FIG. 2 is a cross-sectional view taken substantially along line II-II of FIG. 1;

FIG. 3 is a cross-sectional view, on an enlarged scale, of a rotor part according to the invention; and

FIG. 4 illustrates the stacking of rotor parts on a support rod for application of a dry film lubricant and for other processing.

Reference numeral 10 generally designates a ceramic switch assembly constructed in accordance with the principles of this invention.

The switch 10 has two sections 11 and 12 which, as illustrated, are of substantially identical construction each having a multiplicity of terminals which are interconnected in a particular manner under control of a rotatable operating shaft 13. It will be understood that the contact arrangements and the number of sections may be changed according to the switching functions to be performed in the application for which the switch is designed.

The illustrated section 11 comprises a rotor disc 14 of ceramic material which is tightly fitted on and keyed to an end portion of the shaft 13 having two opposite flat portions 15 for indexing and keying. A small recess 17 in the central opening 16 is provided for visual orientation.

An arcuate contact segment 19 is carried from the front side of the rotor disc 14 and simultaneously engages six out of l2 contacts 20 formed integrally on the ends of clips 21 secured by rivets 22 on a stator disc 24 of ceramic material. If desired, a similar contact segment 25 may be carried from the rearward side of the rotor disc 14 to engage contacts 26 formed on the ends of clips 27 which are secured to thie rearward side of the stator disc 24. It will be understood that although front'and back contact assemblies are illustrated, the design may be such that only one is provided and it will be further understood that different contact arrangements may be used, according to the switching operations to be performed.

The stator disc 24 of the assembly 11 and the stator disc of the assembly 12 are supported from a plate 30 by means of a pair of bolts 31 with suitable spacer sleeves 32 being disposed on the bolts 31. The plate 30 is supported from a sleeve 34 which journals the shaft 13 and which carries a plate 35 disposed to the rear of the plate 30. Plate35 has an opening which receives a detent ball 36, urged toward the plate 30 by a spring plate 37. The plate 30 is formed with twelve rearward projections 38 between which the ball 36 engages to releasibly lock the shaft 13 in a selected angular position.

it is desirable that different forms of contacts be attachable to the rotor'disc 14, as required, and in the illustrated arrangement, the rotor disc 14 is provided with twelve openings 40 in equiangularly spaced relation and at equal radial distances from the central axis, which receives tabs 41 extending from the inner edges of the segment 19.

To insure good electrical contact, the contacts and the clips 21 integral therewith are formed of a suitable resilient metal and in the unstressed condition thereof, the contacts 20 extend to the rear of the plane of the front surface of the segment 19 so as to obtain a pressure engagement between the contacts and the segment 19. As illustrated, the'stator disc 24 has radially extending slots 42 therein, aligned with the contacts 20 and defining radially inwardly projecting fingers 43 therebetween. The inner end surface portions of the fingers 43 are disposed in proximity to an outer cylindrical edge surface 44 of the rotor disc 14 and are of segmental cylindrical shape. The inner end surface portions of the fingers 43 thus together define an inwardly facing cylindrical surface which is interrupted due to the provision of the slots 42. It will be understood, however, that an uninterrupted inwardly facing cylindrical surface may be provided on the stator disc, by reducing the extent of or by eliminating the slots 42.

In accordance with this invention, a dry film lubricant 45 is affixed to the outer'surface 44 of the rotor disc 14. The lubricant 45 serves to prevent interengagement of the surface 44 with the surface portions on thei ends of the fingers 43, which is very important in preventing abrasive action and in preventing the formation of ceramic dust particles which might otherwise engage between the contacts 20 and 26 and the segments 19 and 25. in addition, the lubricant 45 serves as an electrical insulator and it reduces friction, to reduce the energy required to rotate the shaft 13 from one position to another, as well as to obtain a more uniform and reliable action. The dry film lubricant 45, in eliminating the rubbing of the ceramic disc, obviates a gritting sensation which is unpleasant to the ear and to the touch. Further, with the lubricant 45 it is not necessary to maintain extremely close tolerances, or to critically align and realign the parts, decreasing the labor and expense of manufacture, and extending the life of the switch.

According to a specific feature, the outer surface of the rotor disc 14 is formed with chamfered or beveled edges 46 to which the dry film lubricant 45 is affixed, to minimize the possibility of peeling of the lubricant from the rotor disc during assembly, and to otherwise improve the durability and effectiveness of the lubricant.

in accordance with a further feature of the invention, the lubricant is heat bonded to the surface of the ceramic disc 14. One preferred type of composition is a tetrafluoroethylene material (teflon) which may be bombined with either a bonding resin material or with a water base with modifiers. Another preferred type of composition is a molybdenum, tungsten or other metal sulfide combined with a sodium silicate or with isopropanol. Although other types of compositions might be used, the following are given as examples:

EXAMPLEI gested in the product data sheet of the manufacturer. It is found, however, that the film can be treated at a substantially higher temperature, on the order of 550 F. to obtain unexpected results including better adhesion or bonding of I the material to the ceramic, and superior lubricating qualities. Apparently, a major portion of the resin is, driven off at the elevated temperature. The treatment at the elevated temperature is preferably performed after initially baking the material at a temperature of approximately 300 F. in accordance with the manufacturers data sheet.

EXAMPLE [I A colloidal tetrafluoroethylene resin is combined with an epoxy resin solution, preferably with a solids content of 50 percent tetrafluoroethylene and 50 percent of the resin, and a liquid dispersion so obtained is sprayed or otherwise applied to the surface of the ceramic part, after which it is baked at a temperature of approximately 350 F. for 1 hour. The dispersion material may be that marketed under the Trademark EM- RALON 315, a product of the Acheson Colloids Company and the baking temperature of 350 F. is suggested by the manufactueres data sheet. Here again, the treatment at an elevated temperature, on the order of 550 F may be performed to obtain improved and unexpected results.

EXAMPLE Ill Colloidal molybdenum disulfide is combined with sodium silicate and water, preferably with the solids content of the molybdenum disulfide being 20 percent, and the liquid dispersion so obtained is sprayed or otherwise applied to the surface of the ceramic part, after preheating the part to a temperature of approximately 350 F., the film being cured by drying in air. The molybdenum disulfide material is marketed as No. 206 by the Acheson Colloids Company.

EXAMPLE iv This example is the same as example ill except that isopropanol is substituted for the sodium silicate and water, and the preheating of the ceramic part is not performed. The dispersion is available as dispersion No. 210 of the Acheson Colloids Company. 1

EXAMPLE v This example is the same as example lll, except that a tungsten disulfide is substituted for the molydbenum disulfide, the dispersion being available from Acheson Colloids Company as dispersion EC-232l.

EXAMPLE V] This example is the same as example IV, except that a tungsten disulfide is substituted for the molybdenum disulfide, the dispersion being available as dispersion EC-2325 of the Acheson Colloids Company.

EXAMPLE Vll Tetrafluoroethylene combined with 30 to 50 percent of water plus modifiers is sprayed or otherwise applied as a liquid dispersion to the surface of the ceramic part, is allowed to air dry for l5 minutes and is fused at a temperature on the order of from 725 to 800 F. for 15 to 25 minutes. The dispersion is available as No. 851-204 of E. I. DuPont de Nemours Company.

Of these seven examples, the composition of examples 1 and 2 appear to give the best test results, with regard to obtaining a low coefficient of friction, electrical insulation characteristics, temperature ranges of surface, surface adhesion of the bonding vehicles, abrasive resistance, ease of application and ability to control film thickness. However, the other compositions may be used and may have advantages in specific applications,

Further, with regard to film thickness, the film thickness is preferably on the order of from 0.0004 to 0.0006 inches.

a cylindrical part 50 which is preferably threaded on the rod 48 so that the planar faces of the disc 14 are tightly held together. With the ceramic disc 14 stacked on the carrier rod 48, the dry film lubricant may be sprayed to cover the outer cylindrical surfaces 44 as well as the chamfered or beveled edge portions 46, and they may then be cured, according to one of the examples as setforth above. The disc 14 may then be removed from the carrier rods, and it is noted that the provision of the beveled edges is an advantage in this respect, in that the film thickness is slightly less at the junction between adjacent discs and is more readily broken.

It is noted that the dry film lubricant can be applied to one of the interengageable surfaces of a pair of ceramic parts which are not relatively rotatable but are relatively movable otherwise, such as parts supported for relative reciprocable movement. It is further noted that although the dry film lubricant is applied in the illustrated embodiment to the outer cylindrical surface of the rotor disc 14, it could be applied to the innerend surface portions of the fingers 43 and in applying the lubricant, a plurality of the stator discs 24 could be stacked to place the planar surfaces thereof in firm engagement, with the coating being applied inside the stator parts so stacked.

It will be understood that other modifications and variations may be effected without departing from the spirit and scope of the novel concepts of this invention.

I claim:

1. A ceramic contact-supporting member for an electric switch having a surface for disposition in proximity to a surface of another ceramic contact-supporting member movable relative thereto, and an electrically insulating film incorporating therein a polymeric bonding resin material and a dry lubricant and being permanently coated on and affixed to said surface of said member to prevent abrasive interengagement of said surfaces and to prevent the formation of ceramic dust particles which might otherwise engage between contacts carried by said members.

2. A ceramic member as defined in claim 1 in the form of a rotor disc with said surface being an outer peripheral portion thereof. i

3. A ceramic member as defined in claim 1 with said dry film lubricant comprising a tetrafluoroethylene material.

4. A ceramic part as defined in claim 1 wherein said bonding resin material comprises a phenolic resin material.

5. A ceramic member as defined in claim 1 wherein said bonding resin material comprises an epoxy resin material.

6. A ceramic member as defined in claim I, wherein said dry film lubricant comprises a metal disulfide material.

7. The structure of claim 1 wherein the ceramic member to which said film is affixed is a stator.

8. A ceramic member as defined in claim 1 wherein said film comprises a colloidal dispersion of a dry lubricant in a matrix of a polymeric bonding resin material.

9. In an electric switch including two members of ceramic material and interengageable electrical contacts attached to said members, said members being relatively movable and having interengageable surfaces in close proximity, an electrically insulating film incorporating therein a polymeric bonding resin and a dry lubricant and being permanently coated on and affixed to one of said surfaces to prevent abrasive interengagement of said surfaces and to thereby prevent the formation of ceramic dust particles which might otherwise engage between said electrical contacts.

10. In an electric switch as defined in claim 9, said ceramic members being in the form of relatively rotatable discs and said surfaces being generally concentric inner and outer facing surface portions of said discs.

11. A ceramic contactsupporting member for an electric switch having a surface for disposition in proximity to a surface of another ceramic supporting member movable relative thereto, and a dry electrically insulating film coated on and permanently bonded to the surface of said member, said film incorporating a polymeric bonding resin material and a dry lubricant, said polymeric bonding resin being at least partially decomposed, said film being effective to prevent abrasive interengagement of said ceramic contact-supporting member surfaces to prevent the formation of ceramic dust particles which might otherwise become disposed between the contacts carried by said members.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent Nb. 3,553,394 Dated Ja 5A 1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 3, line 1, "releasibly should be releasably Column 4, line 19, "manufactuere's" should be manufacturer's Column 4, line 44, "molydbenum" should be molybdenum Column 4, line 63, "composition" should be compositions IN CLAIM 6:

Delete "film" from the second line in this claim.

Signed and sealed this 15th day of May 1973.

(SEAL) EDWARD M. FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patent 

1. A ceramic contact-supporting member for an electric switch having a surface for disposition in proximity to a surface of another ceramic contact-supporting member movable relative thereto, and an electrically insulating film incorporating therein a polymeric bonding resin material and a dry lubricant and being permanently coated on and affixed to said surface of said member to prevent abrasive interengagement of said surfaces and to prevent the formation of ceramic dust particles which might otherwise engage between contacts carried by said members.
 2. A ceramic member as defined in claim 1 in the form of a rotor disc with said surface being an outer peripheral portion thereof.
 3. A ceramic member as defined in claim 1 with said dry film lubricant comprising a tetrafluoroethylene material.
 4. A ceramic part as defined in claim 1 wherein said bonding resin material comprises a phenolic resin material.
 5. A ceramic member as defined in claim 1 wherein said bonding resin material comprises an epoxy resin material.
 6. A ceramic member as defined in claim 1, wherein said dry film lubricant comprises a metal disulfide material.
 7. The structure of claim 1 wherein the ceramic member to which said film is affixed is a stator.
 8. A ceramic member as defined in claim 1 wherein said film comprises a colloidal dispersion of a dry lubricant in a matrix of a polymeric bonding resin material.
 9. In an electric switch including two members of ceramic material and interengageable electrical contacts attached to said members, said members being relatively movable and having interengageable surfaces in close proximity, an electrically insulating film incorporating therein a polymeric bonding resin and a dry lubricant and being permanently coated on and affixed to one of said surfaces to prevent abrasive interengagement of said surfaces and to thereby prevent the formation of ceramic dust particles which might otherwise engage between said electrical contacts.
 10. In an electric switch as defined in claim 9, said ceramic members being in the form of relatively rotatable discs and said surfaces being generally concentric inner and outer facing surface portions of said discs.
 11. A ceramic contact-supporting member for an electric switch having a surface for disposition in proximity to a surface of another ceramic supporting member movable relative thereto, and a dry electrically insulating film coated on and permanently bonded to the surface of said member, said film incorporating a polymeric bonding resin material and a dry lubricant, said polymeric bonding resin being at least partially decomposed, said film being effective to prevent abrasive interengagement of said ceramic contact-supporting member surfaces to prevent the formation of ceramic dust particles which might otherwise become disposed between the contacts carried by said members. 